A two-dimensional structure in which carbon atoms are regularly arranged in hexagon configuration is called a graphene sheet. A substance formed by stacking a plurality of the graphene sheets is called graphite. The graphene sheet and the graphite have been known. A single sheet of graphene sheet can have been taken out onto a substrate recently (for example, see Non patent document 1), so that the graphene sheet has suddenly attracted attention.
A graphene sheet shows metallic properties because a π band and a π* band contact at the K points in the reciprocal lattice space. Therefore, the graphene sheet is not applicable for electronic devices such as transistors or light-receiving and light-emitting devices such as LEDs.
A lot of computations have been done, and as a result it has been shown that a band gap is generated when a size or an edge structure of a graphene sheet satisfies certain conditions (for example, see Non patent document 2).
However, methods for controlling the band gap using microfabrication technologies have not been found.